This invention relates to a method of manufacturing of optical devices, and in particular, though not exclusively, to manufacturing integrated optical devices or optoelectronic devices, for example, semiconductor optoelectronic devices such as laser diodes, optical modulators, optical amplifiers, optical switches, optical detectors, and the like. The invention further relates to Optoelectronic Integrated Circuits (OEICs) and Photonic Integrated Circuits (PICs) including such devices.
Quantum Well Intermixing (QWI) is a process which has been reported as providing a possible route to monolithic optoelectronic integration. QWI may be performed in III-V semiconductor materials, eg Aluminium Gallium Arsenide (AlGaAs) and Indium Gallium Arsenide Phosphide (InGaAsP), which may be grown on binary substrates, eg Gallium Arsenide (GaAs) or Indium Phosphide (InP). QWI alters the band-gap of an as-grown structure through interdiffusion of elements of a Quantum Well (QW) and associated barriers to produce an alloy of the constituent components. The alloy has a band-gap which is larger than that of the as-grown QW. Any optical radiation (light) generated within the QW where no QWI has taken place can therefore pass through a QWI or xe2x80x9cintermixedxe2x80x9d region of alloy which is effectively transparent to the said optical radiation.
Various QWI techniques have been reported in the literature. For example, QWI can be performed by high temperature diffusion of elements such as Zinc into a semiconductor material including a QW.
QWI can also be performed by implantation of elements such as silicon into a QW semiconductor material. In such a technique the implantation element introduces point defects in the structure of the semiconductor material which are moved through the semiconductor material inducing intermixing in the QW structure by a high temperature annealing step.
Such QWI techniques have been reported in xe2x80x9cApplications of Neutral Impurity Disordering in Fabricating Low-Loss Optical Waveguides and Integrated Waveguide Devicesxe2x80x9d, Marsh et al, Optical and Quantum Electronics, 23, 1991, s941-s957, the content of which is incorporated herein by reference.
A problem exists with such techniques in that although the QWI will alter (increase) the band-gap of the semiconductor material post-growth, residual diffusion or implantation dopants can introduce large losses due to the free carrier absorption coefficient of these dopant elements.
A further reported QWI technique providing intermixing is Impurity Free Vacancy Diffusion (IFVD). When performing IFVD the top cap layer of the III-V semiconductor structure is typically GaAs or Indium Gallium Arsenide (InGaAs). Upon the top layer is deposited a silica (SiO2) film. Subsequent rapid thermal annealing of the semiconductor material causes bonds to break within the semiconductor alloy and Gallium ions or atomsxe2x80x94which are susceptible to silica (SiO2)xe2x80x94to dissolve into the silica so as to leave vacancies in the cap layer. The vacancies then diffuse through the semiconductor structure inducing layer intermixing, eg in the QW structure.
IFVD has been reported in xe2x80x9cQuantitative Model for the Kinetics of Compositional Intermixing in GaAsxe2x80x94AlGaAs Quantumxe2x80x94Confined Heterostructuresxe2x80x9d, by Helmy et al, IEEE Journal of Selected Topics in Quantum Electronics, Vol 4, No 4, July/August 1998, pp 653-660, the content of which is incorporated herein by reference.
Reported QWI, and particularly IFVD methods, suffer from a number of disadvantages, eg the temperature at which Gallium out-diffuses from the semiconductor material to the silica (SiO2) film.
It is an object of at least one aspect of the present invention to obviate or at least mitigate at least one of the aforementioned disadvantages/problems in the prior art.
It is also an object of at least one aspect of the present invention to provide an improved method of manufacturing an optical device using an improved QWI process.
According to a first aspect of the present invention, there is provided a method of manufacturing an optical device, a device body portion from which the device is to be made including a Quantum Well (QW) structure, the method including the step of:
processing the device body portion so as to create extended defects at least in a portion of the device portion.
Each extended defect may be understood to be a structural defect comprising a plurality of adjacent xe2x80x9cpointxe2x80x9d defects.
Preferably said step of processing the device body portion comprises sputtering from the device body portion.
In said step of sputtering from the device body portion a magnetic field may be provided around the device body portion.
In said step of sputtering from the device body portion, a magnetron sputterer may be used.
In said step of sputtering from the device body portion a (reverse) electrical bias may be applied across an electrode upon which the device body portion is provided so as to provide a xe2x80x9cpre-etchxe2x80x9d or cleansing of the device body portion.
In a preceding implementation the method may include the preferred step of depositing a dielectric layer on at least one other portion of the device body portion.
The dielectric layer may therefore act as a mask in defining the at least one portion.
The method may also include the subsequent step of depositing a further dielectric layer on the dielectric layer and/or on the at least one portion of the device body portion.
Advantageously the dielectric layer and/or the further dielectric layer may be deposited by use of a magnetron sputterer. Alternatively, the dielectric layer and/or the further dielectric layer may be deposited by a deposition technique other than by use of a diode sputterer, eg Plasma Enhanced Chemical Vapour Deposition (PECVD). By either of these deposition techniques low damage dielectric layer(s) is/are provided which do not substantially affect an adjacent portion of the device body portion.
The dielectric layer(s) may beneficially substantially comprise silica (SiO2); or may comprise another dielectric material such as Aluminium Oxide (Al2O3).
Preferably, the sputterer includes a chamber which may be substantially filled with an inert gas such as Argon, preferably at a pressure of around 2 xcexcm of Hg, or a mixture of Argon and Oxygen, eg in the proportion 90%/10%.
The step(s) of depositing the dielectric layer(s) may comprise part of a Quantum Well Intermixing (QWI) process used in manufacture of the device.
The QWI process may comprise Impurity-Free Vacancy Disordering (IFVD)
Preferably, the method of manufacture also includes the subsequent step of annealing the device body portion including the dielectric layer at an elevated temperature.
It has been surprisingly found that by sputtering from the device body portion as a step in a QWI technique such as IFVD, preferably by use of a magnetron sputterer, damage induced extended defects are introduced into the at least one portion of the device body portion; the at least one portion may, for example, comprise at least a part of a top or xe2x80x9ccappingxe2x80x9d layer. It is believed that the damage arises due to breakage of bonds in the capping layer before annealing, eg the application of thermal energy by rapid thermal annealing, thereby inhibiting transfer of Gallium from the at least one portion, eg into the further dielectric layer.
Preferably the method of manufacture also includes the preceding steps of:
providing a substrate;
growing on the substrate:
a first optical cladding layer;
a core guiding layer including a Quantum Well (QW) structure; and
a second optical cladding layer.
The first optical cladding layer, core guiding layer, and second optical cladding layer may be grown by Molecular Beam Epitaxy (MBE) or Metal Organic Chemical Vapour Deposition (MOCVD).
In a preferred embodiment the method may comprise the step of:
depositing the dielectric layer on a surface of the device body portion;
defining a pattern in photoresist on a surface of the dielectric layer and lifting off at least part of the photoresist so as to provide the dielectric layer on said at least one other portion of the device body portion.
In said preferred embodiment, the method may also include the step of:
depositing the further dielectric layer on a portion of the surface of the device body and on a surface of the dielectric layer prior to annealing.
In said preferred embodiment, the dielectric layer may comprise an intermixing cap; while the at least one portion of the device body portion and/or the further dielectric layer may comprise an intermixing suppressing cap.
The thickness of the dielectric layer(s) may be around 10 to a few hundred nm.
A subsequent annealing step may occur at a temperature of around 700xc2x0 C. to 1000xc2x0 C. for around 0.5 to 5 minutes, and in one embodiment at substantially 800xc2x0 C. for around 1 minute.
According to a second aspect of the present invention there is provided a method of manufacturing an optical device, a device body portion from which the device is to be made including a Quantum Well (QW) structure, the method including the step of:
sputtering from the device body portion.
Preferably the step of sputtering from the device body portion is carried out using a magnetron sputterer.
According to a third aspect of the present invention there is provided an optical device fabricated from a method according to either of the first or second aspects of the present invention.
The optical device may be an integrated optical device or an optoelectronic device.
The device body portion may be fabricated in a III-V semiconductor materials system.
In a most preferred embodiment the III-V semiconductor materials system may be a Gallium Arsenide (GaAs) based system, and may operate at a wavelength(s) of substantially between 600 and 1300 nm. Alternatively, in a less preferred embodiment the III-V semiconductor materials system may be an Indium Phosphide based system, and may operate at a wavelength(s) of substantially between 1200 and 1700 nm. The device body portion may be made at least partly from Aluminium Gallium Arsenide (AlGaAs), Indium Gallium Arsenide (InGaAs), Indium Gallium Arsenide Phosphide (InGaAsP), Indium Gallium Aluminium Arsenide (InGaAlAs) and/or Indium Gallium Aluminium Phosphide (InGaAlP).
The device body portion may comprise a substrate upon which are provided a first optical cladding layer, a core guiding layer, and a second optical cladding layer.
Preferably the Quantum Well (QW) structure is provided within the core guiding layer.
The core guiding layer, as grown, may have a smaller band-gap and higher refractive index than the first and second optical cladding layers.
According to a fourth aspect of the present invention there is provided an optical integrated circuit, optoelectronic integrated circuit (OEIC), or photonic integrated circuit (PIC) including at least one optical device according to the third aspect of the present invention.
According to a fifth aspect of the present invention there is provided a device body portion (xe2x80x9csamplexe2x80x9d) when used in a method according to either the first or the second aspects of the present invention.
According to a sixth aspect of the present invention there is provided a wafer of material including at least one device body portion when used in a method according to either of the first or second aspects of the present invention.
According to a seventh aspect of the present invention there is provided a sputtering apparatus when used in a method according to the second aspect of the present invention.
Preferably the sputtering apparatus is a magnetron sputterer.
According to an eighth aspect of the present invention there is provided use of a sputtering apparatus in a method according to either of the first or second aspects of the present invention.